Vaso-occlusive devices or implants are used for a wide variety of reasons, including treatment of intra-vascular aneurysms. A common vaso-occlusive device takes the form of a soft, helically wound coil formed by winding a platinum (or platinum alloy) wire strand about a primary mandrel. The relative stiffness of the coil will depend, among other things, on its composition, the diameter of the wire strand, the diameter of the primary mandrel, and the pitch of the primary windings. The coil is then wrapped around a larger, secondary mandrel, and heat treated to impart a secondary shape. For example, U.S. Pat. No. 4,994,069, issued to Ritchart et al., describes a vaso-occlusive coil that assumes a linear, helical primary shape when stretched for placement through the lumen of a delivery catheter, and a folded, convoluted secondary shape when released from the delivery catheter and deposited in the vasculature.
In order to deliver the vaso-occlusive coils to a desired site, e.g., an aneurysm, in the vasculature, it is well-known to first position a small profile, delivery catheter or micro-catheter at the site using a steerable guidewire. Typically, the distal end of the micro-catheter is provided, either by the attending physician or by the manufacturer, with a selected pre-shaped bend, e.g., 45°, 90°, “J”, “S”, or other bending shape, depending on the particular anatomy of the patient, so that it will stay in a desired position for releasing one or more vaso-occlusive coil(s) into the aneurysm once the guidewire is withdrawn. A delivery or “pusher” wire is then passed through the micro-catheter, until a vaso-occlusive coil coupled to a distal end of the pusher wire is extended out of the distal end opening of the micro-catheter and into the aneurysm. The vaso-occlusive device is then released or “detached” from the end pusher wire, and the pusher wire is withdrawn back through the catheter. Depending on the particular needs of the patient, another occlusive device may then be pushed through the catheter and released at the same site.
One known way to release a vaso-occlusive coil from the end of the pusher wire is through the use of an electrolytically severable junction, which is a small exposed section or detachment zone located along a distal end portion of the pusher wire. The detachment zone is typically made of stainless steel and is located just proximal of the vaso-occlusive device. An electrolytically severable junction is susceptible to electrolysis and disintegrates when the pusher wire is electrically charged in the presence of an ionic solution, such as blood or other bodily fluids. Thus, once the detachment zone exits out of the catheter distal end and is exposed in the vessel blood pool of the patient, a current applied to the conductive pusher wire completes a circuit with an electrode attached to the patient's skin, or with a conductive needle inserted through the skin at a remote site, and the detachment zone disintegrates due to electrolysis.
One perceived problem with current embolic detachment schemes is that the junction between the delivery wire and the occlusive member (e.g., coil) can be relatively long and stiff. For example, various intermediate coils and PET bonding joints between the distal end of the delivery wire and the occlusive coil add stiffness to the overall structure. A stiff junction between the delivery wire and the occlusive member complicates accurate placement of the delivery system at the desired location. For example, a stiff section of the delivery wire or the delivery wire/coil junction can cause a pre-shaped micro-catheter to kick back or recoil from the aneurysm upon coil release.
Another perceived problem with some current embolic detachment devices is that a separate return or ground electrode is used to complete the electrical circuit between the external power supply and the electrolytically detachable coil. This separate return or ground electrode may be a patch that is placed on the patient's body or a needle that is inserted into the patient's groin area. The use of a separate, return or ground electrode does, however, introduce variability into the detachment time(s) of the occlusive coils. Variability is produced because of different tissue types and densities that exist between the occlusive device and the return electrode. Also, for grounding needles that are placed in the groin area of the patient, some patients experience discomfort or pain.
There thus is a need for a vaso-occlusive delivery system that reduces the overall length and stiffness of the junction between the delivery wire and the occlusive coil. Such a system should be easy to use yet provide for consistent detachment of embolic elements in the desired location. Moreover, the delivery system should be able to release the embolic element without extensive movement or kick-back motion resulting from the detachment operation. There is also a need for a vaso-occlusive delivery system that reduces variability in detachment times for occlusive devices. In this regard, there also is a need for alternative return or ground electrode configurations that do not utilize a separate, external return electrode such as a patch or grounding needle.